REALLY?; The Claim: With a runny nose, green calls for an antibiotic.

By ANAHAD O'CONNOR

Published: October 6, 2009

THE FACTS Old prescription habits apparently die hard.

Studies have suggested that most doctors say they would prescribe an antibiotic if a child with sinus symptoms also had green nasal discharge. The habit stems from the notion that green indicates a bacterial infection.

But other studies show that green is no more common in a bacterial infection than a viral one, for which antibiotics are ineffective.

In a definitive study from 1984, scientists put 142 children with green nasal discharge into groups, including one that was treated with antibiotics and another that received a placebo. They found that the drugs had no effect on ''potentially pathogenic organisms'' or on symptoms. About 35 percent of subjects treated with antibiotics showed improvement, compared with 31 percent in the placebo group. More recent studies have bolstered that conclusion.

According to the Centers for Disease Control and Prevention, when cold viruses infect the respiratory tract, the body makes clear mucus that helps wash away germs from the nose and sinuses. After about three days, the body's immune cells fight back, changing the discharge to a white or yellow color. ''As the bacteria that live in the nose grow back, they may also be found in the mucus, which changes to a greenish color,'' the agency says. ''This is normal.''

The only time antibiotics are needed for a runny nose, experts say, is when the diagnosis is bacterial sinusitis.

THE BOTTOM LINE The color of nasal discharge should not dictate the medicine.